1. Field of the Invention
The present invention relates to a digital filter circuit used in audio, a voice memorandum, etc., and particularly to a decimation filter.
2. Description of the Related Art
A decimation filter is a circuit wherein data such as voice is partly thinned out to thereby carry out its compression. There is also known a decimation filter that has the function of removing noise produced due to its compression. The conventional decimation filter is capable of processing single-channel data or data of multi-channel each having the same sampling period. The prior art has been described in, for example, Japanese Unexamined Patent Publication No. Hei 8 (1996)-32409 and Japanese Unexamined Patent Publication No. 2003-264451.
However, only the single conventional decimation filter cannot process data of multi-channel having different sampling periods. When the multi-channel data having the different sampling periods are processed using the conventional decimation filter, it is necessary to match their sampling frequencies with one another before the respective data of multi-channel are inputted to the decimation filter or provide decimation filters every channels. When the former method is used, degradation in sound quality due to the frequency matching-up occurs. When the latter method is used, a circuit scale increases.